1. Field
The following description relates to a network synchronization method and apparatus for performing a time synchronization between nodes.
2. Description of Related Art
A variety of schemes to transmit timing between nodes of a network using time stamps exist.
In such schemes, each of nodes constituting the network attempts time synchronization with a single node among the nodes included in the network. The single node is known as a grandmaster. Specifically, in such schemes, timings is traceable to a grandmaster.
Each node, except for the grandmaster node, contains a single slave port and possibly one or more master ports. The grandmaster node contains one or more master ports, but no slave ports. Master ports transmit messages including time stamps to all nodes connected to the master ports. For example, the time stamps may be the time when the messages are transmitted. If the port at the other end of the link attached to a master port is a slave port, it receives the time stamp and adds the propagation time between the slave port and the master port to the time stamp. The slave port also time stamps the message on receipt, relative to its local clock. Then, the node that contains the slave port, i.e., the slave node, compares the received time stamp with propagation time added with the time stamp of the message on receipt. The slave node then computes the offset, i.e., the difference between the time stamp of the message on receipt and the received time stamp with propagation time added, and thereby perform a time synchronization. In this instance, the offset corresponds to the difference between master node and slave node time. Each node that sends messages through a master port to synchronize a slave node is known as a master node. Each master node, except for the grandmaster, is also a slave node to another master node.